-- | General XML stuff.
--
module Xml (
- FromXml(..),
+ DtdName(..),
+ ToFromXml(..),
parse_opts,
- pickle_unpickle )
+ pickle_unpickle,
+ unpickleable )
where
+import Control.Exception ( SomeException(..), catch )
+import Database.Groundhog ( AutoKey )
import Text.XML.HXT.Core (
(>>>),
(/>),
+ PU,
SysConfigList,
XmlPickler(..),
hasName,
-- Groundhog type from the XML one. But Groundhog won't use type family
-- instances, so here we are.
--
-class FromXml a where
+class ToFromXml a where
-- | Each instance a must declare its associated XML type (Xml a)
type Xml a :: *
+ type Container a :: *
-- | And provide a function for getting an (Xml a) out of an "a."
to_xml :: a -> Xml a
+ -- | And provide a function for getting an "a" out of an (Xml a).
+ from_xml :: Xml a -> a
+
+ -- | Often we need to provide a key to use as a foreign key into
+ -- some container. If the instance "belongs" to some other object,
+ -- then it might need to be passed a key before it can un-XML
+ -- itself. For example, the XML version of 'NewsTeam' doesn't
+ -- contain a message ID which is part of its database type.
+ from_xml_fk :: AutoKey (Container a) -> Xml a -> a
+ from_xml_fk _ = from_xml
+
+
+-- | Represents the DTD filename ("SYSTEM") part of the DOCTYPE
+-- definition.
+newtype DtdName = DtdName String
-- | A list of options passed to 'readDocument' when we parse an XML
-- document. We don't validate because the DTDs from TSN are
parse_opts =
[ withPreserveComment no,
withRemoveWS yes,
- withSubstDTDEntities no,
- withValidate no ]
+ withSubstDTDEntities no ]
-- | Given a root element name and a file path, return both the
-- to 'xpickle' would be ambiguous. By returning some @a@s, we allow
-- the caller to annotate its type.
--
+-- Note that this will happily pickle nothing to nothing and then
+-- unpickle it back to more nothing. So the fact that the
+-- before/after results from this function agree does not mean that
+-- the document was successfully unpickled!
+--
pickle_unpickle :: XmlPickler a
=> String
-> FilePath
pickle_unpickle root_element filepath = do
-- We need to check only the root message element since
-- readDocument produces a bunch of other junk.
- expected <- runX $ arr_getobj
+ expected <- runX arr_getobj
actual <- runX $ arr_getobj
>>>
xpickleVal xpickle
hasName root_element
>>>
xunpickleVal xpickle
+
+
+
+-- | Is the given XML file unpickleable? Unpickling will be attempted
+-- using the @unpickler@ argument. If we unilaterally used the
+-- generic 'xpickle' function for our unpickler, a type ambiguity
+-- would result. By taking the unpickler as an argument, we allow
+-- the caller to indirectly specify a concrete type.
+--
+unpickleable :: XmlPickler a => FilePath -> PU a -> IO Bool
+unpickleable filepath unpickler = do
+ xmldoc <- try_unpickle `catch` (\(SomeException _) -> return [])
+ return $ (not . null) xmldoc
+ where
+ try_unpickle = runX $ readDocument parse_opts filepath
+ >>>
+ xunpickleVal unpickler